I had an ebpf program which calls a kfunc defined and implemented in one of my kernel modules, it was working fine in 6.16, but was rejected to run by libbpf in 6.19, the error message was: libbpf: extern (func ksym) 'bpf_strstr': func_proto [5] incompatible with vmlinux [94389] The reason is there is a new added kfunc in kernel 6.19 which happens to be the same name with my kfunc. However the error message is not obvious enough to address problem immediately. Therefore, this patches searches duplicated kfunc in both btf_vmlinux and btf_modules list before a kernel module attempts to register kfuncs through register_btf_kfunc_id_set, it prints clear error message and returns error code if same name kfunc has already implemented and registered, then developer knows at the first place. Suggested-by: Alexei Starovoitov Suggested-by: Kaitao Cheng Signed-off-by: Song Chen --- changelog: v1 --- v2: libbpf has already specified which module this kfunc belongs to as ebpf code onwer's expectation, then verifier uses find_kallsyms_symbol_value to search kfunc's addr. v2 --- v3: After v2, I tried a new idea of introducing a namespace in libbpf to specify kfunc owner in an ebpf program suggested by Kaitao Cheng, please see [1]. Alex suggested to go back to report an error during kmod load on conflicting kfunc name for now. What's more, v2 only searched bpf_vmlinux, v3 also traverses btf_modules list. [1]:https://lore.kernel.org/all/CAADnVQ+jYGMjAC9aNygmhyppUO9foWN4z9cjSpwCEXAFHpRVJQ@mail.gmail.com/ --- kernel/bpf/btf.c | 44 +++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 43 insertions(+), 1 deletion(-) diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c index 4872d2a6c42d..a14ad3720872 100644 --- a/kernel/bpf/btf.c +++ b/kernel/bpf/btf.c @@ -8618,6 +8618,47 @@ static int btf_check_iter_kfuncs(struct btf *btf, const char *func_name, return 0; } +static int btf_check_kfunc_name(struct btf *btf, const char *func_name, u32 kind) +{ +#ifdef CONFIG_DEBUG_INFO_BTF_MODULES + struct btf_module *btf_mod, *tmp; +#endif + s32 id; + int ret = 0; + + if (!btf_is_module(btf)) + goto out; + + id = btf_find_by_name_kind(bpf_get_btf_vmlinux(), + func_name, kind); + if (id >= 0) { + pr_err("kfunc %s (id: %d) is already present in vmlinux.\n", + func_name, id); + ret = -EINVAL; + goto out; + } + +#ifdef CONFIG_DEBUG_INFO_BTF_MODULES + mutex_lock(&btf_module_mutex); + list_for_each_entry_safe(btf_mod, tmp, &btf_modules, list) { + if (btf_mod->btf == btf) + continue; + id = btf_find_by_name_kind(btf_mod->btf, + func_name, kind); + if (id >= 0) { + pr_err("kfunc %s (id: %d) is already present in module %s.\n", + func_name, id, btf_mod->module->name); + ret = -EINVAL; + break; + } + } + mutex_unlock(&btf_module_mutex); +#endif + +out: + return ret; +} + static int btf_check_kfunc_protos(struct btf *btf, u32 func_id, u32 func_flags) { const struct btf_type *func; @@ -8631,7 +8672,8 @@ static int btf_check_kfunc_protos(struct btf *btf, u32 func_id, u32 func_flags) /* sanity check kfunc name */ func_name = btf_name_by_offset(btf, func->name_off); - if (!func_name || !func_name[0]) + if (!func_name || !func_name[0] + || btf_check_kfunc_name(btf, func_name, BTF_INFO_KIND(func->info))) return -EINVAL; func = btf_type_by_id(btf, func->type); -- 2.43.0